mailmap: update email address for Guo Ren

The ren_guo@c-sky.com would be deprecated and use guoren@kernel.org as the
main email address.

Link: https://lkml.kernel.org/r/20211123022741.545541-1-guoren@kernel.org
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>